1. Field of the Invention
The invention relates to a mask frame and elbow for use with a mask system for Non-invasive Positive Pressure Ventilation (NPPV) and for continuous positive airway pressure (CPAP) therapy of sleep disordered breathing (SDB) conditions such as obstructive sleep apnea (OSA).
2. Background of the Invention
The use of NPPV for treatment of SDB, such as OSA was pioneered by Sullivan (see, for example, U.S. Pat. No. 4,944,310, the contents of which are hereby incorporated in their entirety by reference). Apparatus for this treatment involves a blower which delivers a supply of air at positive pressure to a patient interface via an air delivery conduit. The patient interface may take several forms such as nasal masks and nose and mouth masks. Patients must wear a mask all night while sleeping to receive the therapy. Masks typically comprise a rigid shell or frame and a soft face-contacting cushion that spaces the frame away from the face and forms a seal with the patient's face. The frame and cushion define a cavity which receives the nose, or nose and mouth. The mask is held in position by headgear, which usually comprises an arrangement of straps that passes along the side of the face to the back or crown of the head.
Kwok et al. (U.S. Pat. No. 6,112,746), the contents of which are hereby incorporated in their entirety by reference, describe a nasal mask and mask cushion. The mask cushion is a substantially triangularly shaped frame from which extends a membrane. The mask frame has a scalloped edge by which the mask cushion is affixed to a mask frame. The membrane has an aperture into which the user's nose is received. The membrane is spaced away from the rim of the frame, and its outer surface has substantially the same shape as the rim.
Frater et al. (PCT Patent Application AU01/00746, published as WO 01/97893), the contents of which are hereby incorporated in their entirety by reference, describes a mask system for delivering air to a user includes a suspension mechanism to allow relative movement between a face-contacting cushion and a mask frame. The suspension mechanism also provides a predetermined force to the cushion that is a function of mask pressure, displacement of the cushion, or both.
During the course of the respiratory cycle patients inhale air, largely comprising a mixture of nitrogen and oxygen, and exhale a mixture of gases including a relatively higher fraction of CO2. In a nasal mask system where the patient breathes through the nose, there can be a build-up of CO2 in the mask cavity which can lead to undesirable CO2 re-breathing. Hence a variety of vents have been developed for use with masks. The amount of CO2 in the mask cavity is a function of vent geometry, mask geometry, flow patterns within the mask and the amount of dead-space within the mask cavity.
The mask is typically joined to the air delivery conduit using a friction fit. Since the blower is typically placed beside a patient's bed, it is typical that the air delivery conduit be at least 1 meter long. Occasionally, movement of the air delivery conduit can disrupt the seal. Furthermore, some patients prefer to have the conduit in one position (for example passing over their heads), whereas other patients prefer to have it in another position (for example to the left or right side). Hence swivel elbows were developed for some masks.
Swivel elbows typically include: (i) a cylindrical first portion, having an axis aligned in a first direction and being adapted for connection to an air delivery conduit; and (ii) a cylindrical second portion, having an axis aligned in a second direction and being adapted for connection to a frame of a mask.
The first and second directions typically are at right angles to one another. The first portion has an outer diameter slightly smaller than the inner diameter of typical air delivery conduit tubing, so that the tubing can overfit the first portion and be held in position by friction. A free end of the second portion is adapted to pass through an orifice in the mask frame. Such known swivel elbows typically include a vent. While some vents are simply holes, such as those in the Puritan-Bennett SOFTFIT mask (FIG. 10a), others are more sophisticated, such as those used with the ResMed ULTRA MIRAGE® mask.
A problem with the prior art swivel elbows incorporating a simple vent, such as the Puritan-Bennett SOFTFIT (FIG. 10a), the Respironics CONTOUR-DELUXE (FIG. 10c) and the related art Tiara ADVANTAGE elbows (FIG. 10b), is that air from the blower can simply short-circuit the mask and pass straight out of the vent. This is a particular problem when a patient is being given supplemental oxygen, which is expensive. A significant portion of the oxygen being fed to the elbow simply passes out the vent without entering the mask.
FIGS. 8a, 8b, 9a, and 9b show prior art elbows manufactured by ResMed Limited for the STANDARD and MODULAR masks respectively. FIGS. 8c, 8d, 9c, and 9d show related art elbows manufactured by ResMed Limited for the ULTRA MIRAGE® and MIRAGE® VISTA masks respectively. FIGS. 11a to 11f show prior art elbows in the WHISPER swivel I and swivel II masks manufactured by Respironics. FIGS. 12 and 13 show a prior art mask SERENITY mask manufactured by DeVilbiss in which the interior of the nasal cavity includes a baffle B for redirecting incoming gas.
A mask that includes a cushion with a gusset will have a larger cavity, and hence more dead-space than a mask without a gusset, everything else being equal. Hence in a mask assembly with a gusset, particular attention needs to be paid to venting the mask to ensure that sufficient CO2 is washed out by a continuous influx of fresh air.
Since the mask is to be used by sleeping users, it is also desirable to reduce or eliminate noise from all sources, including those caused by the venting of gases from the mask.
Kwok (PCT/AU98/00067, published as WO 98/34665), the contents of which are hereby incorporated in their entirety by reference, describes a mask and a vent. In one form the vent comprises a soft flexible insert piece with a series of orifices.
Drew et al. (PCT/AU00/00636 published as WO 00/78381), the contents of which are hereby incorporated in their entirety by reference, disclose a connector that comprises a mask end for connecting, in fluid communication, with the interior of a respiratory mask and a supply conduit end disposed at an angle to the mask end for connecting, in fluid communication, with the outlet of a breathable gas supply conduit. The connector also includes a gas washout vent passage having an inlet adjacent to, or forming part of, the mask end in fluid communication with the interior of the respiratory mask and an outlet in fluid communication with the atmosphere. The outlet includes an interior surface that forms a smooth prolongation with an adjacent exterior surface of the connector. The vent outlet is disposed on the side of the connector remote the mask end, has a generally part-annular cross section and is adapted to direct the washout gas in direction substantially perpendicular to the longitudinal axis of the mask end and substantially parallel to the longitudinal axis of the supply conduit end towards the supply conduit end.
Moore et al. (co-pending provisional application serial No. 60/402,509, filed Aug. 12, 2002), the contents of which are hereby incorporated in their entirety by reference, describe a mask system including a swivel elbow with a vent.
Correa et al. (U.S. Pat. No. 6,119,694) discloses a nasal mask assembly with a miniature nare seal. The mask assembly includes a conduit receptor that attaches to a gas delivery tube. Downstream of the conduit receptor is a bore that receives a stem having opposed flanges. The flanges separate the incoming gas into a plurality of channels, such that the gas is provided to one of a plurality of spatial regions in the interior of the nare seal.
While the vents and connectors described in the previous references provide adequate intake of breathable air/gas and venting for masks that have a small amount of dead-space, e.g., without gussets, they may be inadequate to provide air intake and CO2 removal in masks that have larger amounts of dead-space, e.g., with gussets. Therefore, there exists a need in the art for a swivel elbow and mask assembly that overcome the problems listed above.